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Simple extensions to Guava library with a Scala flavour

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/**
 * Copyright 2012 Julien Eluard
 * This project includes software developed by Julien Eluard: https://github.com/jeluard/
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.github.jeluard.guayaba.lang;

import com.google.common.base.Preconditions;
import com.google.common.collect.AbstractIterator;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * Helper metchods for {@link Iterable}.
 */
public final class Iterables2 {

  private Iterables2() {
  }

  /**
   * Encapsulates a {@code value} from an {@link Iterable} with its associated {@code index}.
   * @param  
   */
  public static final class Indexed {

    public final int index;
    public final T value;

    public Indexed(final int index, final T value) {
      this.index = index;
      this.value = Preconditions.checkNotNull(value, "null value");
    }

  }

  /**
   * Augment iterated value with an `index` corresponding to its position in the {@link Iterable}.
   *
   * @param 
   * @param iterable
   * @return 
   */
  public static  Iterable> withIndex(final Iterable iterable) {
    Preconditions.checkNotNull(iterable, "null iterable");

    return new Iterable>() {
      @Override 
      public Iterator> iterator() {
        return new AbstractIterator>() {
          private final Iterator iterator = iterable.iterator();
          private int index = 0;
          @Override
          protected Indexed computeNext() {
            try {
              return new Indexed(this.index++, this.iterator.next());
            } catch (NoSuchElementException e) {
              //Don't rely on hasNext/next as this would complexify concurrent access support.
              return endOfData();
            }
          }
        };
      }
    };
  }

}